Evaluation of the antagonistic effect of six mixed cultures of lactic acid bacteria, isolated from the Ethiopian fermented milk ergo, against some foodborne pathogens inoculated into the Ethiopian cottage cheese ayib

The antagonistic effect of mixed lactic acid bacterial cultures against foodborne pathogens (Staphylocuccus aureus ATCC 25923, Shigella boydii clinical isolate, Pseudomonas aeruginosa ATCC 25853) was evaluated in pasteurized ayib stored at room temperature. The lactic acid bacteria (LAB) were tested for acid tolerance at pH 2.0, 2.5, 3.0 and 3.5 for three and six h and for bile tolerance for 24 and 48 h at 0.3% (w/v) bile salt concentration. Their antimicrobial effect on selected foodborne pathogens was assessed by co-culturing assays in laboratory medium. The effect of mixed LAB cultures against the foodborne pathogens tested was followed in ayib stored at ambient conditions for 9 days. Only 11 LAB isolates were isolated upon their survival at a pH value of 3.5. Out of the 11 LAB isolates selected from a total of 60 based on their survival at pH 3.5, 6 isolates showed survival at pH 2.5 and pH 3.0 for 3 h with survival rates of 1.03-22% and 5-100%, respectively. The same 6 LAB isolates displayed tolerance to 0.3% bile salt concentration for up to 48 h. In the presence of acid-bile tolerant LAB isolates as compared to the control (without any LAB bacteria), Ps. aeruginosa was inhibited by all six to varying degree while, Sh. boyidii and S. aureus were inhibited by five of the LAB in laboratory medium. The mixed LAB culture was inoculated in to pasteurized ayib which was stored at ambient temperature for nine days and completely eliminated Ps. aruginosa, S. aureus and Sh. boyidii from day 5, 6, and 7, respectively. The result indicates that the mixed acid-bile tolerant LAB cultures eliminated the test pathogens in both laboratory medium and in ayib. The mixed acid-bile tolerant LAB culture could possibly be used as candidate potential protective starter culture for preparation of ayib.